1. Field
Exemplary embodiments of the present invention relate to an analog-to-digital converter and an analog-to-digital conversion method and, more particularly, to a technology for improving the accuracy of an analog-to-digital converter.
2. Description of the Related Art
As the size of a complementary metal-oxide-semiconductor (CMOS) device is reduced, the power supply voltage is also rapidly reduced. From the standpoint of a digital circuit, such a decrease in the power supply voltage is advantageous in that switching power is reduced, but since the signal-to-noise ratio (SNR) deteriorates due to the reduction in the analog circuit signal swing, circuit design becomes more difficult.
There are various types of analog-to-digital converters that convert output values of the analog circuit to digital values used in the digital circuit. Among them, a flash analog-to-digital converter (flash ADC), a pipe line analog-to-digital converter (pipe line ADC), an over-sampling analog-to-digital converter using delta-sigma conversion, and the like are used in application fields according to the respective characteristics thereof. In the analog-to-digital converters other than the flash analog-to-digital converter, an operational amplifier is used. However, as the power supply voltage is reduced, it is difficult to design operational amplifiers. Therefore, analog-to-digital converters without operational amplifiers have been researched. An analog-to-digital converter without an operational amplifier includes a voltage-controlled oscillator (VCO)-based analog-to-digital converter. In VCO-based analog-to-digital converters, a voltage-controlled oscillator, which is the most important block, is easily affected by Process, Voltage, and Temperature (PVT) variation.